Effective utilization of electric power has been called for against the recent trend of global warming. As one of means of effective utilization of electric power, secondary batteries for electric power energy storage have been expected, and from a viewpoint of air pollution prevention, it has been expected that large-size secondary batteries are put to practical use early as a power source for automobiles. Also, particularly, with the proliferation and the performance improvement of electrical equipment, such as digital cameras and cellular phones, the demand of small-size secondary batteries as a power source for backup for computers and the like, or as a power source for small-size electrical household appliances is increasing steadily year by year.
As these secondary batteries, there is required a secondary battery having a performance corresponding to electrical equipment to be used, and, generally, lithium ion batteries are mainly used.
The lithium ion battery is configured such that a negative-electrode material in which a negative-pole active substance, such as graphite, adheres to a negative-electrode substrate made of copper foil; a positive-electrode material in which a positive-pole active substance, such as lithium nickelate or lithium cobaltate, adheres to a positive-electrode substrate made of aluminum foil; a collector made of aluminum or copper; a separator made of a resin film, such as a polypropylene porous film; and an electrolytic solution, an electrolyte, and the like are enclosed inside an exterior can made of metal, such as aluminum or iron.
While the demand of lithium ion batteries is increasing, establishment of a countermeasure against environmental pollution due to used lithium ion batteries has been strongly desired, and the recovery and effective use of valuable metals have been considered.
As a method for recovering valuable metals from a lithium ion battery having the above-mentioned structure, dry treatment or incineration treatment, such as treatments disclosed in PTL 1 and PTL 2, has been used. However, these methods have disadvantages that consumption of thermal energy is large and, moreover, lithium (Li) and aluminum (Al) can not be recovered. Furthermore, there is a problem that, in the case where lithium hexafluorophosphate (LiPF6) is contained as an electrolyte, a furnace material is greatly consumed.
For these problems of such dry treatment or incineration treatment, there has been proposed a method for recovering valuable metals by wet treatment, as disclosed in PTL 3 and PTL 4. As this method by wet treatment, there has been proposed a method such that all the materials resulting from dismantling of a lithium ion battery is dissolved by using an acidic solution or the like to recover valuable metals. However, in the case of this total dissolution method, a chemical agent is consumed for elements which excessively exist, such as aluminum, copper (Cu), iron (Fe), and the like, and therefore the method is not economical for effectively recovering valuable metals, such as nickel (Ni), cobalt (Co), lithium, and the like.
To solve this problem, there has been proposed a wet treatment by a selectively-peeling-off method, wherein a positive-electrode material is selectively peeled off from a lithium ion battery, and valuable metals are efficiently recovered from the positive-electrode material. In the method of selectively peeling off a positive-electrode material, a first chemical treatment is such that a positive-pole active substance containing valuable metals is peeled off from a positive-electrode substrate (positive-electrode foil) (Al, and the like). Conventionally, in this peeling-off treatment of a positive-pole active substance, an acidic solution, such as a sulfuric acid solution, or an alkaline solution, such as a sodium hydroxide solution, has been used. A solution to be used in this step of separating a positive-pole active substance contains a large amount of an electrolytic solution, an organic substance, and the like, each of which becomes an obstacle to subsequent recovery of valuable metals, whereby wastewater treatment is needed. Therefore, it is preferable that valuable metals are not allowed to dissolve in the solution.
However, in this peeling-off step, when an acidic solution, such as a sulfuric acid solution, is used, part of valuable metals contained in positive-pole active substance dissolve, thereby causing a recovery loss of the valuable metals.
Also, there is a problem that, when an acidic solution or an alkaline solution is used to separate a positive-pole active substance, the separated positive-pole active substance agglomerates, thereby being insufficiently separated from a positive-electrode material. This is considered because, when a positive-electrode material reacts to an added acid or an added alkali, a part of the positive-electrode material dissolves to generate hydrogen gas, and a positive-pole active substance adheres around the generated gas bubbles. Furthermore, the agglomerate of the positive-pole active substance easily adheres also to a positive-electrode material which should be separated, and therefore, for example, it is difficult to mechanically separate the positive-pole active substance from the positive-electrode material at a downstream step, thereby causing a lower recovery rate of the positive-pole active substance.
Thus, a separation treatment of a positive-pole active substance in the conventional method for recovering valuable metals from a lithium ion battery by wet treatment not only caused a recovery loss due to dissolution of valuable metals, but also caused agglomeration of a positive-pole active substance, thereby hindering a positive-pole active substance from being sufficiently separated from a positive-electrode material, and thus led to a lower recovery rate of the positive-pole active substance. This also caused a lower recovery rate of valuable metals.